A typical inkjet printer uses one or more printheads. Each printhead typically contains an array of individual nozzles for ejecting drops of ink across an open gap to an image receiving member to form an image. The image receiving member may be a continuous web of recording media, a series of media sheets, or the image receiving member may be a rotating surface, such as a print drum or endless belt. Images printed on a rotating surface are later transferred to recording media by mechanical force in a transfix nip formed by the rotating surface and a transfix roller. In an inkjet printhead, individual piezoelectric, thermal, or acoustic actuators generate mechanical forces that expel ink through an orifice from an ink filled conduit in response to an electrical voltage signal, sometimes called a firing signal. The amplitude, or voltage level, of the signals affects the amount of ink ejected in each drop. The firing signal is generated by a printhead controller in accordance with image data. An inkjet printer forms a printed image in accordance with the image data by printing a pattern of individual ink drops at particular locations on the image receiving member. The locations where the ink drops landed are sometimes called “ink drop locations,” “ink drop positions,” or “pixels.” Thus, a printing operation can be viewed as the placement of ink drops on an image receiving member in accordance with image data.
One factor affecting the registration of images printed by different groups of printheads is printhead alignment. In some printers, multiple printheads are configured to enable the printheads to print a continuous line or bar on media in a cross-process direction. Aligning the printheads so the nozzles at one end of a printhead, such as the right end of the printhead, are spaced from nozzles at the other end of another printhead, such as the left end of the printhead, by a distance that is approximately the same as adjacent nozzles within a printhead is important for registration. Printheads arranged in a column also need to be aligned to enable a second printhead in the column in the process direction to eject ink drops onto or next to ink drops ejected by a first printhead in the column.
Currently, printers include controllers that receive image data of printed test patterns and analyze that image data to identify the positions and orientations of printheads. The controllers then identify distances that the printheads can be moved to compensate for differences between the actual positions of the printheads and their expected positions. These identified distances are used to generate signals for operating actuators that move either an individual printhead or a group of printheads to correct for displacement of the printhead or printheads. In some printers, the actuators that move individual printheads are smaller and less reliable than the actuators that move groups of printheads. If one of these smaller actuators need to be replaced, the entire printing system has to be halted and the motor replaced before accurately registered printing can resume. Consequently, addressing the reliability of the actuators that enable a controller to move printheads to compensate for misalignment of printheads in a printer is important.